1. Field of the Invention
The present invention relates to a signal analyzer, more particularly to a signal analyzer for analyzing dynamic behavior of a target system.
2. Description of the Related Art
Signal analysis is widely used in electrical power equipment, communication, energy management, and system stability. By signal analysis, a system model of a target system can be established for analyzing steady, transient and dynamic behavior of the target system.
Currently, signal analysis is generally divided into time-domain and frequency-domain methods. Regarding the frequency-domain methods, a group power method based upon Parserval's theorem is used to calculate a dynamic signal (C. S. Moo, Y. N. Chang, and P. P. Mok, “A Digital Measurement Scheme for Time-varying Transient Harmonics,” IEEE Trans. Power Delivery, vol. 10, No. 2, April 1995, pages 588-594). The group power method can conveniently and quickly find amplitudes of harmonics. Furthermore, an interpolated Fast Fourier Transform method uses band parameters to analyze accurate harmonic parameters that include frequency, amplitude and phase parameters of harmonics (V. K. Jain, W. L. Collins, Jr., and D. C. Davis, “High-accuracy Analog Measurements via Interpolated FFT,” IEEE Trans. Instrument Measurements, vol. IM-28, No. 2, June 1979, pages 113-122). However, all the frequency-domain methods need sufficient data. Therefore, ability of the frequency-domain methods for analyzing the dynamic signal will be limited.
Relatively, the time-domain methods only need few data to calculate signal parameters. Therefore, the time-domain methods are suitable for analyzing dynamic signals. For example, the Gauss method has a succinct structure to analyze signal parameters, and an optimization method uses least mean square to restrain disturbance from noise (H. C. So and Y. T. Chan, “Analysis of an LMS Algorithm for Unbiased Impulse Response Estimation,” IEEE Trans. Signal Processing, vol. 51, pages 2008-2013, July 2003). In practice, the disturbance exists in a time-domain signal, and the disturbance may significantly affect analyzing result. For reducing the disturbance, an amount of the data used in the time-domain methods is required to be increased. However, ability of real-time operation will weaken when the required amount of the data is increased. Therefore, it is hard to achieve accuracy and real-time operation in signal analysis at the same time.